1. Field of the Invention
The invention relates to an emergency call system for a motor vehicle, having a transmitter, provided in the motor vehicle, for automatically transmitting an emergency call to an external receiving station, and having a signal generator, the transmitter and the signal generator being connected to an arithmetic and logic unit which activates the emergency call if there is an appropriate signal from the signal generator, and to a method for automatically transmitting an emergency call from a motor vehicle to a receiving station using a transmitter.
2. Background of the Invention
Such an emergency call system is disclosed in WO 90/03899. A signal from a signal generator triggers an automatic emergency call. The signal generator can be an air bag, an alarm system or a temperature or gas sensor. The system can therefore activate an alarm using a mobile radio device in the event of the vehicle having a collision or being stolen, depending on the signal generator used. In addition, the emergency call system contains a navigation unit for determining and transmitting the position of the vehicle together with the emergency call. Further information, such as vehicle-related data, vehicle type, dangerous goods class, the telephone number, an accident report, a fire warning and the number of vehicle occupants can be transmitted with the emergency call. A disadvantage of this system, however, is that, in the event of a collision, the emergency call device can become damaged and is therefore sometimes inoperable. This means that the emergency call can no longer be transmitted.
The object of the invention is therefore to specify an emergency call system which avoids this disadvantage and ensures that the emergency call is transmitted reliably. A further object of the invention is to specify a method for automatically transmitting an emergency call from a motor vehicle to a receiving station.
The former object is achieved in an emergency call system of generic type in that the emergency call system contains means for determining a probability level for an imminent accident using the signals from the signal generator, and the emergency call can be activated if a limit value for the probability level is exceeded.
In particular, the emergency call system contains, as the signal generator, measuring means connected to the arithmetic and logic unit for determining the relative speed and the distance of the motor vehicle in relation to another vehicle or an obstacle, in which case the arithmetic and logic unit can perform a comparison between the relative speed determined using the measuring means and a maximum permissible value for the relative speed at the measured distance, and the emergency call can be activated if the maximum permissible relative speed for a given distance is exceeded. The emergency call can thus be activated even before an accident or a collision between the motor vehicle and another vehicle or an obstacle.
The method according to the invention is distinguished in that the distance and the relative speed of the motor vehicle in relation to another vehicle or an obstacle are ascertained, the relative speed ascertained is compared with a defined, maximum permissible relative speed for the distance ascertained, and an emergency call is triggered if the particular relative speed of the motor vehicle exceeds the defined, maximum permissible relative speed.
In the known emergency call system described in the introduction, the emergency call is transmitted only if a sensor registers a collision. For this purpose, the air bag signal is used, for example. In contrast to this, the emergency call system according to the invention can be used to establish that the collision is no longer avoidable even before it occurs. Consequently, the emergency call can therefore also be activated even before the collision occurs, that is to say at an instant when the emergency call system is still operable. To this end, the relative speed of the motor vehicle in relation to another vehicle or an obstacle is determined in the same way as the distance of the motor vehicle from the other vehicle or obstacle. If the relative speed exceeds a predetermined value for a given distance, it can be assumed that a collision is unavoidable.
Hence, for each distance between the motor vehicle and another vehicle or an obstacle, a maximum permissible limit value is defined for the relative speed. This limit value can be determined in the arithmetic and logic unit using a defining equation for the respective distance. However, it is also possible to store a plurality of value pairs, in each case for a distance and an associated maximum permissible relative speed, in a memory element, the memory element being connected to the arithmetic and logic unit. The arithmetic and logic unit then retrieves the value pairs which are nearest to the current distance and uses them to determine the maximum permissible relative speed of the vehicle, for example by means of interpolation.
In addition, there may be a variety of such limit values for the maximum permissible relative speed. By way of example, these can allow for the attributes of the road. Thus, a higher limit value is permissible, for example, for a dry road than for a wet road or snow-covered road. To determine the attributes of the road, the vehicle must be provided with appropriate sensors. As an example, dry and wet roads can be distinguished optically using the portion of light reflected from the road.
Although, in principle, it is also possible to locate the motor vehicle transmitting an emergency call, the vehicle position is preferably transmitted to the receiving station together with the emergency call. To this end, the vehicle is provided with, in particular, a navigation system which is known per se, in which case the position can be determined in a known manner using both satellite navigation (GPS navigation) and dead-reckoning navigation. Amongst the various functions of a navigation system, only position determination is of importance to the emergency call system, and not route calculation. Hence, it is also sufficient, for example, to use only a receiver with an evaluation unit for GPS navigation, rather than a full navigation system.
To prevent false alarms, in one particular embodiment, the arithmetic and logic unit in the emergency call system is connected to at least one sensor for detecting an accident. The emergency call system also contains a timer which is connected to the arithmetic and logic unit and is started when the emergency call is activated. If there is no signal signaling a collision from the sensor at the instant the timer runs out, the emergency call is automatically revoked.
If, for example, a driver still manages to steer clear of an obstacle and thus avoid a collision despite the relative speed being above the limit value, the revocation of the emergency call prevents auxiliary forces from being alerted. The sensor for detecting an accident can, in particular, be an acceleration sensor or a temperature sensor. Since acceleration sensors are already provided for releasing the air bag in motor vehicles, it is particularly advantageous if the emergency call system is connected to said acceleration sensors. Thus, if the air bag is not released by the time the timer runs out, it is assumed that there has been no collision and the emergency call is revoked. So that the revocation of the emergency call is not dependent on the signal from an individual sensor, a plurality of sensors can be provided. If a temperature sensor is provided, a vehicle fire, in particular, can also be registered.
To activate a sufficient number of rescue forces, a further provision, in a preferred embodiment, is that the arithmetic and logic unit in the emergency call system is connected to seat-occupancy sensors, so that the number of occupied motor vehicle seats can be transmitted with the emergency call.
An important integral part of the emergency call system according to the invention are the measuring means for determining the relative speed and the distance of the motor vehicle in relation to another vehicle or an obstacle. Preferably, these measuring means are based on the evaluation of a transmitted and received, reflected radar signal. Although such radar systems are not yet in standard use in motor vehicles, the expert is aware of them. The use of radar systems for providing distance warnings and for regulating distance in motor vehicles is described in Walliser et al.: Elektronik im Kraftfahrzeugwesen [Motor Vehicle Electronics], 2nd edition, Expert-Verlag, Renningen-Malsheim 1997, pages 308 to 331. Radar systems have the advantage over optical or acoustic methods that attenuation due to rain and mist is low. Possible frequencies specified are 35 GHz and 78 GHz.
In addition, WO 94/16340 describes a computerized radar method for measuring distances and relative speeds between a vehicle and obstacles in front of it. In this method, radar signals are transmitted which are reflected by another vehicle or an obstacle. The reflected radar signals are in turn picked up and evaluated. The relative speed between the motor vehicle containing the system and another vehicle or obstacle is determined on the basis of the Doppler shift in the frequency of the transmitted and reflected signals. Since the radar signal is transmitted in pulsed form, the timing of the pulse can be used to ascertain the distance between the motor vehicle and the vehicle or obstacle reflecting the radar pulse. To distinguish between actual obstacles and apparent obstacles reliably, the method described in the aforementioned patent application can be used, for example.
Any known radio system can be used for transmitting the emergency call. To ensure reliable transmission of the emergency call, this system should have universal coverage, however. On account of the fact that mobile radio systems based on the GSM standard are already very widespread in Europe, these systems are particularly preferred here, as are systems based on the more recent UMTS standard. These can be the known D and E networks, for example. Corresponding systems are sufficiently well known to the expert and are also established for use in motor vehicles, so that there is no need for them to be described in more detail here.